Patients with RA (n = 52) and patients with BD, (n = 40) as another systemic inflammatory disease, were studied along with a systemically healthy control group (HC; n = 57). Full mouth periodontal parameters were recorded. RA activity was assessed using the 28-joint DAS-28. RFs-IgM and -IgA were measured using ELISA. GCF samples were investigated by using fluorescent in situ hybridization for 10 different bacterial taxa. The gene discussed is CD40LG; the disease is Behcet disease.